Elucidating the molecular basis of synaptic plasticity will lead to a more sophisticated understanding of the neural circuit modifications which underlie experience-dependent plasticity in both health and disease. Much is known about the mechanisms of postsynaptic forms of long lasting plasticity. By comparison, however, relatively little is known about the mechanisms of presynaptic plasticity. This proposal focuses on understanding the synaptic functions of a class of presynaptic, active zone proteins, RIMs, because of their requirement in a prominent form of presynaptic LTP and their additional roles in basal neurotransmitter release and short-term plasticity. RIMs have several protein binding domains that interact with key components of synaptic vesicles and active zones. Because of this, RIMs have been described as presynaptic "scaffold" proteins. As a scaffold, RIM is a powerful tool to gain insight to the coordinate activities of several important presynaptic proteins. A key outstanding question is to understand how RIM integrates the activities of its binding partners to achieve synaptic plasticity. In this proposal, we will perform rescue experiments in the RIM1a knockout background to delineate the functional significance of RIM1a's interactions with other presynaptic proteins. We will also study the functional significance of a key PKA phosphorylation site that is implicated in mediating LTP. Lastly, we will evaluate the functional significance of the RIM2 gene products. Are they functionally redundant or does expression of a particular RIM isoform convey distinct synaptic properties? To perform these experiments we will use electrophysiological recording techniques on both culture and acute slice preparations in combination with molecular techniques to allow gene transfer into the knockout background. A precise understanding of the molecular interactions that underlie presynaptic plasticity as described in this proposal is critical both to enable studies of the behavioral significance of presynaptic plasticity and to enable targeting these proteins for the development of therapies for a wide range of neuropsychiatric diseases that may involve synaptic plasticity such as dementia, dystonia and addiction.